Although this site is dedicated to firearms, I thought I would post an effectiveness comparison of the various self defense tools.  These are guns, Tasers, pepper spray, and edges/blunt objects.


Pistol
Guns
Pros: The most effective way to stop an attacker yet invented by humans.  Works up close, and at a distance.  Can be less expensive than a Taser.
Cons: More expensive than pepper spray.

I consider firearms to be the most effective means of self defense.  This is because a gun can reach out and stop an attacker from across the room, or when they are only inches away.  A gun allows more “shots” than a Taser (which usually only offer 1 or 2), and wind/close quarters wont’ cause the gun to incapacitate its owner the way pepper spray can.  Guns work by disrupting an attacker’s vital organs in such as way to to physically stop them from continuing their attack.  This means that an attacker cannot become desensitized to bullets the way they could become desensitized to the pain and irritation from pepper spray.  Thick clothing is generally not bulletproof, while a thick leather coat could defeat a Taser.  A separate article discusses the selection of a gun for home defense.


Taser
Tasers
Pros: Sometimes allowed in areas where gun are banned.  Virtually no risk to bystanders.
Cons: Limited capacity for follow-up shots, limited ability to penetrate thick clothing, reduced effectiveness at keeping an attacker down

Tasers and similar stun gun devices either propel a pair of dart-tipped electric wires toward the attacker, or rely upon the Taser being placed in contact with the attacker.  An electric charge is then delivered to the attacker, in order to incapacitate them.  Leaving aside the controversy regarding the safety of Tasers, I’ll address their effectiveness in self defense.  My thoughts are that while Tasers are more effective than pepper spray, and sure beat throwing rocks, they are less effective than guns.  This is because of their limited capacity for follow-up shots in the event of miss, their reduced ability to penetrate thick clothing, and their reduced effectiveness at keeping an attacker down.
Unlike firearms, which often have magazines which hold 6 to 20 rounds, Tasers typically hold 1 or 2 shots.  When a law abiding citizen is awoken in the night by a home invader, the combination of having just awoken, the dark, and stress can make even the most accurate person miss.  Having the extra shots that most firearms provide can mean the difference between life and death.  I also believe that Tasers are less effective than firearms due to their limited ability to penetrate clothing.  If a home invader were to break in wearing a heavy leather jacket, with additional clothing underneath, the Taser’s darts might not penetrate, while a bullet would penetrate and stop the attacker.  Finally, the ability of an attacker to get back up after being Tasered concerns me.  Since the amount of time that a Taser will incapacitate a person varies by individual, a Tased individual could get back up and continue their attack, possibly at a time when the home owner is unable to Taser them again.
For those reasons, I believe that a gun is a better self defense tool than a Taser, but that is not to say that Tasers are a bad thing for self defense.  I would much rather have a Taser than, say, a baseball bat, a pointy stick, or a bucket full of rocks :) .  Tasers do have the great advantage of virtually no risk to innocent bystanders.  While a bullet can pass through a wall and kill an innocent bystander, Tasers won’t injure those on the other side of a wall.


Pepper Spray
Pepper Spray
Pros: Inexpensive, Low risk to bystanders.
Cons: Less effective than a gun or a Taser, risk of blowback onto the user.

The active ingredient in pepper spray is capsaicin, which is the chemical compound that makes peppers spicy.  Pepper spray is a concentrated form of capsaicin, and some pepper sprays also include tear gas.  When pepper spray contact the eyes, nose, mouth, and even skin of an attacker, it causes swelling and pain, which is intended to incapacitate the attacker.  While pepper spray can be effective, I consider pepper spray less effective than a gun because it is shorter ranged, and because it relies upon the attacker feeing enough pain to make them want to quit the attack.  While some pepper sprays claim an effective reach of 20 feet, this is still well short of that which any gun offers, and many pepper sprays will only work effectively at much closer distances.  Pepper spray can cause swelling and involuntary closing of the eyes in some people, however there are plenty of people who can continue to attack even after being pepper sprayed, or whose eyes are swollen closed but continue to blindly attack.  Attackers under the influence of drugs may be virtually immune from the effects of pepper spray as well.  A final concern is the risk of blowback or contamination.  Pepper spray can be blown back on to the person who used it, and it can be transferred by physical touch.  This could leave the law abiding citizen incapacitated at the worst possible time (and some people, such as those with asthma, are especially sensitive to pepper spray).  Like Tasers, pepper spray does have the huge advantage of not endangering the lives of nearby innocent bystanders the way a firearm can, should the shooter miss and send a bullet through a wall to an occupied room.


Knife
Blunt or Edged Objects
Pros: Often inexpensive and easily acquired
Cons: Generally the least effective option for self defense

Tools such as baseball bats, golf clubs knives, swords, are melee weapons, rather than the ranged weapons discussed above.  As such, blunt or edged weapons require that the person using these weapons get very close to the criminal.  Since the criminal will often have a gun, the person defending themselves may be shot before they can even get close enough to their attacker to act in self defense.  For example, if a criminal breaks in and points a gun at a home owner from across the room, a baseball bat is not of much help.  Similarly, if a criminal breaks in and surprises a home owner who is in their bed, a golf club is not going to save that person.  Also, these weapons rely upon the user having sufficient physical strength and room to swing the object.  This means that an 85 year old woman would likely not be able to use a baseball bat to defend herself – but she could effectively use a gun.

Conclusion
There is a reason that police and the military have guns, rather than relying exclusively upon pepper spray, Tasers, or blunt/edged objects – and that reason is that guns remain the most effective means of stopping a violent attacker.  That is not to say that Tasers, Pepper spray, and blunt or edged objects don’t have their place, but in a life or death situation I would prefer a gun over any of those choices.  If you are unsure which home defense gun to select, this article may help.  If gun safety is unfamiliar to you, see this article.  If you are concerned about overpenetration of bullets in a home defense situation, this article may help.  In some limited situations where guns were not allowed, or where the risk of overpenetration by bullets was extreme, pepper spray or a Taser could be the next-best option to a gun.